1. Field of the Invention
The present invention relates to a tool clamping device for clamping a variety of tools selectively received in a tool spindle which is carried in a spindle head of a machine tool.
2. Description of the Prior Art
A prior art tool clamping device of this type is disclosed in Japanese examined, published utility model application No. 55-15942, for example. The known tool clamping device is constructed such that a cylindrical guide member is mounted on the front end of a draw bar which passes through a through bore of a tool spindle in a spring-biased manner. A plurality of steel balls, which are fitted in the circumferential wall of the guide member for movements in the radial directions, are engageable with a pull stud of a tool coaxially fitted in the front end of the tool spindle. The steel balls are also engageable with an inner circumferential surface of the bore of the tool spindle so that radial outward movements of the steel balls are restrained to clamp the tool on the tool spindle. In the tool clamping device constructed as above, when the draw bar is moved toward the front end of the tool spindle against the biasing force of the spring, the steel balls come to face a larger-diameter portion which is formed in the front end portion of the tool spindle bore, so that they can retract toward the radial outside to release the pull stud of the tool. However, it is impossible for the known device to clamp the tool in case the pull stud of the tool is shorter than the moving stroke of the guide member retaining the steel balls. This raises a problem that the prior art tool clamping device cannot be applied to a tool having a short pull stud.